The term "semiconductors" is understood as designating elements, compounds or alloys, the specific electrical resistance of which lies between that of metals and that of insulators, i.e. values of from 10.sup.-4 to 10.sup.+12 .OMEGA.. cm.
Conventional semiconductors consist of silicon, germanium, gallium and arsenic. Moreover, compound semiconductors which are composed of at least two elements are repeatedly described in the literature, for example IIIA-VA compounds which consist of elements of the IIIA and VA Groups or IIB-VIA compounds which consist of elements off the IIB and VIA groups of the Periodic Table of Elements.
Recently, semiconductors have become very significant in commercial terms for electronic and electric construction elements, such as luminescence diodes. Hall probes, capacitors, solar cells, n-p-doped transistors, field effect transistors, bipolar integrated transistors, thyristors or information stores.
Semiconductors which are used as electronic or electric elements frequently have to be provided with an electrically conducting layer. An electrically conducting or ferromagnetic layer may be applied, for example by high vacuum evaporation with metals or by vacuum sputtering with metal oxides. Disadvantages of the resulting products include a poor abrasion resistance and insufficient regularity of the electric and magnetic properties, which are caused by a low adhesiveness and hardness, and by an irregular layer thickness of the metal layer. Moreover, the known metallization processes are labor-intensive and incapable of producing the desirable fine electrical printed lines which have a complicated geometrical structure, during the partial metallization of electrical semiconductors. An object of the present invention is to provide semiconductors with a firmly adhering metal layer, without changing the chemical and physical properties of the semiconductors.
This object is achieved by depositing metals on the surface of the electrical semiconductor by a particular currentless, chemical process, optionally using suitable masks, and the deposited metal may then be reinforced by galvanization.
In currentless chemical metallization processes, the surface of the substrate to be metallized is firstly activated, for which purpose elements of the IB and VIIIB Groups of the Periodic Table are used, for example silver, copper, gold, platinum and, preferably, palladium, which are used as salt solutions (ionic process) or as sols (colloidal process). Activation is followed by reduction of the precious metal ions, if they are still present, after which metallization is carried out in a metallization bath, for example a nickel bath. The substrate surface must always be pickled, for example, by using chromosulphuric acid or other antioxidants before these processes, so that the metal layer adheres effectively to the substrate surface after activation and metallization. A pickling process of this type cannot be used for semiconductors, due to the irreversible change in important properties, for example in the creep resistance of the electrical surface resistance, in the light absorption and in the light perviousness.